How Long Do Symptoms of Fatigue Last in Infectious Mononucleosis?

Persisting Tiredness May Be Due to Other Causes

Chronic fatigue due to mono or infectious mononucleosis rarely persists beyond 6 months and may be due to other sleep disorders like sleep apnea or insomnia
Chronic fatigue due to mono or infectious mononucleosis rarely persists beyond 6 months and may be due to other sleep disorders like sleep apnea or insomnia. Getty Images

Infectious mononucleosis (or mono) is a common infectious disease that may result in symptoms of profound fatigue or tiredness, but how long does the fatigue typically last? What else might cause persisting fatigue? Learn about how mono contributes to fatigue and what other conditions and sleep disorders like sleep apnea to consider if the fatigue is not getting better.

What Causes Mononucleosis?

Mononucleosis is not a sleep disorder per se, but because it is so common and the fatigue can be so debilitating, it is worth a closer look.

It is sometimes called the "kissing disease" due to its transmission via saliva and is characterized by fever, infection of the tonsils or throat, and the swelling of lymph nodes. It is caused by the Epstein-Barr virus (EBV), which is quite common, eventually infecting 90 to 95 percent of all adults. This virus is spread by personal contact. Mono can also be caused by cytomegalovirus (CMV). Mono infections are very common among teenagers and young adults.

As part of this illness, people often experience fatigue that may be persistent and severe. In a study of 150 patients, fatigue resolved slowly and was still present in 13 percent of people at six months. It appears to be more common and severe in women compared to men, especially among college students. 

Severe Symptoms Associated with Mono

In very severe cases, mononucleosis may result in other neurologic symptoms affecting the nervous system.

These can include meningitis and encephalitis, which are infections of the brain or the tissues surrounding the brain and spinal cord called the meninges. When present, this more severe infection might cause confusion, headache, and drowsiness or coma. These complications occur very rarely.

What to Do If Fatigue Is Not Improving

In general, the symptoms of fatigue will gradually resolve over a period of weeks to months.

As noted, in a minority of people, the fatigue may still be present 6 months after the initial infection. If fatigue persists beyond six months, the condition called chronic fatigue syndrome may be entertained, as EBV has been considered as a possible cause of this disorder. It may also be important to look at other sleep disorders that can cause sleepiness and fatigue, including obstructive sleep apnea and insomnia.

If you are struggling with debilitating fatigue or tiredness, speak with your doctor about the need for further evaluation, including testing for sleep disorders. There are effective treatments available and these might help you to feel and function at your best. In rare cases, the use of stimulant medications may be necessary to resolve the fatigue.


Hickie, I et al. "Post-infective and chronic fatigue syndromes precipitated by viral and non-viral pathogens: prospective cohort study." BMJ. 2006;333(7568):575.

Macsween, KF et al. "Infectious mononucleosis in university students in the United Kingdom: evaluation of the clinical features and consequences of the disease." Clin Infect Dis. 2010;50(5):699-706.

Rea, TD et al. "Prospective study of the natural history of infectious mononucleosis caused by Epstein-Barr virus." J Am Board Fam Pract. 2001;14(4):234-42.

Schellinger, PD et al. "Epstein-Barr virus meningoencephalitis with a lymphoma-like response in an immunocompetent host." Ann Neurol. 1999;45(5):659-62.

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